1. Field of the Invention
This invention relates to method and apparatus for evaporating and separating a vaporizable component from a multiple component liquid, such as a solvent-solute liquid, and more particularly to method and apparatus utilizing vertical shell and tube evaporators in combination with mechanical separators for evaporating and separating vaporizable components from a multiple component liquid. The invention has specific application to water pollution control apparatus and method and in particular to method and apparatus for fractionating essentially pure water from solvent-solute, waste solutions or mixtures.
2. Prior Art
In recent years, the nickel and chrome plating industries have become increasingly concerned with compliance with ever-tightening environmental standards, rapidly escalating prices for plating chemicals and shortages of plating chemicals. Due to the environmental standards, plating rinse solutions can no longer be discharged into streams, but must either be destroyed (i.e. rendered non-toxic) or processed to recover portions thereof.
The destruction of plating rinse solution requires the use of costly destruct chemicals to convert toxic portions of the plating rinse solution into a disposable sludge. In that 50 to 90 percent of the plating chemicals are dragged out from the plating tank with the product to be plated and mixed with the rinse solution, the destruction of plating rinse pollutants not only involves the loss of costly destruct chemicals but also the loss of up to 90 percent of the expensive plating chemicals. Also, sludge-removal is becoming more difficult due to the declining number of land-fill sites for sludge disposal.
Accordingly, recovery methods and apparatus have been developed to recover plating chemicals or solutions from plating rinse solutions. Flash evaporators, such as that shown in U.S. Pat. Nos. 3,640,331 and 2,853,442, and ion exchangers, such as that shown in U.S. Pat. No. 3,681,212, have been used for this purpose.
However, known flash evaporators do not produce distilled water of a very high quality, that is, three parts per million (3 ppm) or less of plating metal; but rather the water separated from this type of recovery unit has a purity of 5 to 10 parts per million. Moreover, flash evaporators will not effectively handle solutions containing foaming agents. Also, this type of unit will recover nickel or chrome plating solutions of up to only 50 ounces per gallon. Finally, this unit is bulky and requires up to 80 square feet of floor space and up to 15 feet of ceiling height.
The ion exchange recovery unit will not handle nickel and will not produce a concentration of over 12 ounces per gallon.
Other known types of plating waste recovery units are submerged tube evaporators, atmospheric evaporators, and reverse osmosis systems. The lattermost will not handle chrome; and its recovery of nickel is limited to a maximum concentration of 12 ounces per gallon and to a solution which has little or no foaming agents. Atmospheric evaporators do not recover water; but rather the water evaporated from the rinse solution, together with any toxic liquid entrained therein, are lost to the atmosphere.
Accordingly, no prior known type of recovery unit satisfactorily meets the following requirements for completely effective recovery of plating solution and water: water purity of three parts per million or less of plating metal; recovery of either nickel or chrome plating solutions; capability of handling solutions containing foaming agents; capability of recovering nickel solutions of a concentration of up to 50 ounces per gallon and chrome solutions of 100 and 60 ounces per gallon; and compactness of design permitting use with limited available floor and headroom space.
A major object of this invention is to provide a recovery unit that will satisfy all of these requirements. Moreover, it is an object of this invention to provide a unit that performs reliably in producing essentially pure water and a plating solution of the desired concentration. It is also an object to provide a recovery unit which does not require frequent maintenance and which is relatively chemically durable, that is, which is capable of withstanding corrosion by metallic acid plating solutions.